Expiry vs PAO: What Those Symbols Actually Mean and Why Brands Lowball Them

Every skincare product carries date information, but most consumers misunderstand what these symbols actually mean. The little jar icon with “12M” inside? That’s not the same as an expiry date. And both might be more conservative than necessary — for reasons that have nothing to do with your safety.

The Two Dating Systems

Expiry Date (Best Before): A specific date, usually formatted as MM/YYYY or DD/MM/YYYY. This indicates when the product’s efficacy can no longer be guaranteed, regardless of whether it’s been opened.

PAO (Period After Opening): The open jar symbol with a number and “M” (for months). This indicates how long the product remains stable after first use. A “12M” symbol means 12 months after opening.

These serve different purposes and have different implications.

How PAO Is Actually Determined

Brands don’t pick PAO periods randomly. They’re based on stability testing — specifically, testing how the product performs after being repeatedly opened, exposed to air, and used over time.

Accelerated stability testing exposes products to elevated temperatures, humidity, and light to simulate longer periods in shorter timeframes. Real-time testing monitors products over actual durations.

The PAO period is typically set at the point where testing shows the product remains safe and effective, with a safety margin built in.

Here’s what consumers don’t realise: that safety margin is often substantial.

Why Brands Choose Conservative Dates

A product that tests stable for 18 months might carry a 12M PAO. Why?

Liability protection. If someone develops a reaction or infection at month 13, a 12M PAO means the brand can point to exceeded guidelines. A longer PAO increases legal exposure.

Encouraging repurchase. If your serum says 6M but you’ve only used half the bottle, you’re psychologically prompted to either accelerate use or discard and replace. Shorter PAO periods drive faster repurchase cycles.

Variable storage conditions. Testing occurs under controlled conditions. Your bathroom cabinet might be humid, warm, and subject to temperature fluctuations. Conservative PAOs account for less-than-ideal consumer storage.

Ingredient degradation vs safety. A vitamin C serum might still be safe at month 9 but significantly less potent. Is that “expired”? Brands choose PAOs that reflect when the product might underperform, not when it becomes dangerous.

The Preservative Connection

Products with robust preservative systems can safely last longer than those with weak or natural preservation. But here’s the marketing tension: consumers have been taught to distrust preservatives.

A product with effective synthetic preservatives might be stable for 24+ months after opening. A “preservative-free” or “natural preservation” product might genuinely need a 6M PAO because it’s more vulnerable to contamination.

The products marketed as gentler and cleaner often require more frequent replacement. More purchases per year. The economics align neatly with the marketing.

What Actually Happens Past PAO

Most skincare products don’t become dangerous immediately after their PAO expires. What typically happens:

Efficacy decreases. Actives like vitamin C, retinol, and certain peptides degrade over time. Your serum isn’t harmful; it’s just less effective.

Texture changes. Emulsions can separate. Serums can thicken or thin. Oils can oxidise and change colour or smell.

Preservative effectiveness drops. This is the genuine concern. As preservatives degrade, the product becomes more vulnerable to microbial contamination with each use.

pH shifts. Products formulated at specific pH levels may drift outside their effective range.

For most products, being a month or two past PAO isn’t dangerous. Being a year past, especially with regular use introducing contaminants, becomes genuinely risky.

Expiry Dates and Unopened Products

Expiry dates on unopened products relate to stability during storage, not use. An unopened product kept in reasonable conditions will generally last well beyond its printed expiry date.

The date reflects when the manufacturer guarantees full potency and safety, with the usual conservative margin. An expired but unopened product isn’t automatically worthless — but its efficacy may have diminished.

This matters for sales and samples. That sample you got at a counter might have been sitting there for months. Check the date.

The Batch Code Alternative

Some products show only batch codes, not dates. These typically encode manufacturing date information that consumers can decode online using batch code checkers.

Why use batch codes instead of clear dates? Partly practical (international products with different date format conventions), partly strategic (less obvious product age on shelves), partly just industry convention.

If you want to know how old a product is, batch code lookup sites can help — though brands don’t universally confirm the accuracy of these tools.

Refrigeration Realities

Refrigerating skincare can extend product life by slowing oxidation and preservative degradation. This is particularly valuable for unstable actives like vitamin C.

But refrigeration doesn’t stop the clock. It slows it. And the PAO periods aren’t based on refrigerated storage — they assume room temperature. So refrigerating your vitamin C serum might extend useful life beyond the printed PAO, but by how much? Nobody can say with precision.

The Eye and Lip Product Exception

PAO periods for products used around eyes and lips are typically shorter — often 3-6 months — even when the formulation could last longer.

This reflects the higher contamination risk in these areas and the greater consequences of infection. Eye products in particular carry genuine risk of serious harm if contaminated.

These shorter PAOs are appropriately conservative, not commercially motivated. Respect them.

Practical Interpretation

So how should you actually approach product dates?

With unopened products: The expiry date indicates guaranteed quality. Products modestly past this date are usually fine but may have reduced efficacy. Products significantly past should be discarded.

With opened products: The PAO is a reasonable guideline with built-in margin. A few weeks beyond isn’t concerning for most products. Months beyond warrants caution, especially for products exposed to repeated use, humidity, or warmth.

Signs of actual spoilage: Colour change, smell change, separation, unusual texture, or visible growth all mean immediate disposal regardless of dates.

Product-specific considerations: Vitamin C serums degrade faster than most. Retinols are relatively stable. Oils oxidise at different rates depending on type. Products with applicators that contact skin face higher contamination risk than those dispensed without skin contact.

What Brands Won’t Tell You

No brand will publicly say “our PAO is conservative and you can probably use this longer.” The liability is too high.

But formulation chemists privately acknowledge that commercial PAO periods are often significantly shorter than actual product stability. The 12M product might be fine at 18 months. The 6M product might easily last 9.

This isn’t a recommendation to ignore PAOs — it’s context for understanding that they represent a commercial and legal calculation as much as a scientific one.

The Bottom Line

PAO periods are useful guidelines, not precise expiration moments. They’re set conservatively for liability and commercial reasons, with margins that mean most products are fine somewhat beyond their stated periods.

Use common sense: assess the product visually and by smell, consider storage conditions, and apply greater caution to eye products and contamination-prone formats.

And recognise that when a brand chooses a 6M PAO over a 12M PAO, the decision often serves their business model as much as your safety. The product that makes you repurchase faster isn’t necessarily the product that expires faster — it might just be the product with a more aggressive dating strategy.